Sorce was taken from Wikipedia, so there may be some inaccuracy.
Believe it or not, the airline was founded by American interests in 1978 to provide airline service to West Berlin, a territory that could not legally be served by West German airlines such as Lufthansa due to political restrictions on East German airspace. Air Berlin became a German-owned company in 1991, shortly after the reunification of Germany, and eventually joined the Oneworld alliance in 2012. After years of losses, Air Berlin filed for insolvency on 15 August 2017 and ceased operations on 27 October 2017, yet another airline bit the dust. However, it wasn't all bad news, in 1990–2000: New investors and expansion, German reunification led to significant changes to the European aviation market, and in particular in Berlin: German airlines now gained access to the city. In 1991, Air Berlin with Kim Lundgren, the original founder, brought the ownership in line with German foreign-control requirements. Joachim Hunold (de), a former sales and marketing director with LTU International, now led the company.
Following an order for ten Boeing 737-800s, Air Berlin grew and by 1999, the fleet grew to twelve aircraft. In 2001, Air Berlin and Hapag-Lloyd Flug became the first airlines in the world to have their Boeing 737-800s fitted with blended winglets, and wingtip devices that are intended to improve fuel efficiency.
Air Berlin introduced scheduled flights (which could be booked directly with the airline rather than via a tour operator) in 1997, initially linking a number of secondary German airports to Mallorca. By 2002, 35 percent of Air Berlin's tickets were sold directly. In the same year, the airline expanded beyond holiday destinations as low-fare flights marketed as "City Shuttle" to London, Barcelona, Milan, and Vienna started. Besides Berlin-Tegel, these routes were opened at six German airports (Dortmund, Düsseldorf, Hamburg, Münster/Osnabrück, Nuremberg, and Paderborn/Lippstadt) that until then had not been served by one of the rising European low-cost carriers.
On 28 September 2016, Air Berlin announced The new air-berlin, a restructuring project including the reduction of its destinations from around 140 to 70, the focus on the Berlin and Düsseldorf hubs and on the smaller bases in Stuttgart and Munich, the closure of six other bases, the targeting of business travelers, focus on domestic German flights and on flights to Italy, Scandinavia and eastern Europe, the expansion of its long-haul network, and the loss of up to 1,200 jobs.
Air Berlin, including its subsidiaries Belair and Niki, planned to cut 40 of its fleet of 118 narrowbody jets, leaving Air Berlin with its own fleet of 75 aircraft. The new fleet would be 17 Airbus A330-200 for long-haul operations and 40 Airbus A320 family aircraft and 18 Bombardier Q400 aircraft for European routes. A separate, tourist-destination-oriented unit with 35 aircraft was to be formed, perhaps operating with a partner (TUIfly was the assumed partner as they already operate several aircraft for Air Berlin) – or sold altogether. Plans to wet-lease the remaining aircraft were realized with the December 2016 announcement that 38 Airbus A319/A320 aircraft would be wet-leased to Lufthansa Group's Eurowings (33 aircraft) and Austrian Airlines (five), effective February 2017 for a period of six years.
In October 2016, Air Berlin announced plans to close four of its seven air-berlin Technik maintenance facilities and lay off 500 of its staff.
On 5 December 2016, Air Berlin announced plans to sell its entire 49-percent stake in its Austrian subsidiary Niki to its own minority owner, Etihad Airways. It was also announced that Niki will take over several routes to southern European, north African, and Turkish leisure destinations from Air Berlin as part of the new joint-venture.
After Etihad stopped financial support, Air Berlin entered insolvency procedures on 15 August 2017. On 9 October 2017, Air Berlin told its staff that it would cease all remaining operations under its own AB flight numbers due to its negative financial outlook and bankruptcy proceedings.
On 12 October 2017, Lufthansa agreed to buy 81 aircraft and employ 3,000 Air Berlin employees for €210 million, taking over the subsidiaries Niki and Luftfahrtgesellschaft Walter with a total of 1700 employees.
On 24 October 2017, the Berliner Zeitfracht Group confirmed it would take over the Leisure Cargo Düsseldorf company and its 60 employees. The creditors' committee approved a corresponding submission. Leisure Cargo conveys freight space on passenger flights. On 27 October 2017, it was announced that a 'consortium' of maintenance, repair, and operations provider Nayak Aircraft Services GmbH & Co. KG and Berliner Zeitfracht Group would purchase air-berlin Technik, keeping over 300 employees.
The final long-haul flight, from Miami to Düsseldorf, was operated on 15 October 2017. On 27 October 2017, Air Berlin's final flight was operated by Airbus A320 D-ABNW. It departed from Munich at 21:36 and landed at Berlin Tegel at 22:45.
On 28 October 2017, it was announced that EasyJet would absorb 1,000 employees and lease 25 Airbus A320 aircraft for flights from Berlin Tegel for €40 million.